The long term objective is to understand the neural processes subserving human multijoint arm movement. Both motor and related sensory investigations are proposed. The context for both experimental lines is arm trajectory formation and central computation of hand and joint information. The results will contribute to an improved understanding of the pathophysiology of disorders of movement and proprioception. The aim of the motor studies is to determine the contributions of the ipsilateral and contralateral hemispheres to control of multijoint movement of the arm. The goal is prompted by the reported ability of a cerebral hemisphere to control movement of the ipsilateral arm. The study will involve a comparison of the kinematic properties of arm movements controlled by individual hemispheres in patients who have undergone a therapeutic corpus callosotomy. The subject will be asked to move his hand to a visual target or a target indicated by the location of the unseen opposite hand. An individual hemisphere will be made dominant in the control of an arm by restricting visual target information to the appropriate visual field. Arm movement information will be digitized, and the efficacy of ipsilateral control will be assessed quantitatively. The sensory studies are aimed at determining the type of arm position information which must be present, where it is located, and what pathways contribute to its computation. This will be investigated by observing the ability of corpus callosotomy patients and patients with focal lateralized lesions to detect when certain types of passive movements have been imparted to one or both arms. By using a variety of tasks, position information will be categorized as related to hand location or joint angle. The work will set the stage for learning how position information is used by the motor system.